Inertialess transducer



' sept. 24, 1963 Filed Feb. 27. 1961 w. R. ToRN INERTIAL-Ess TRANsnucER2 Sheets-Sheet 1 sept. 24, 1963 w. R. TORN 3,105,124

INERTIALESS TRANSDUCER Filed Feb. 27. l1961 2 Sheets-Sheet 2 NEW BITUSED FOR FINE FINISHING, THEN USED FOR ROUGH FINISH ON NEXTJOB JOZUnited States Patent C 3,105,124 WERTEALESS TRANSDUCER Wiliiarn R. Tern,St. Charles, lli., assigner to Duitane Corporation, St. Charles, lll., acorporation of Delaware Fiied Feb. 2'7, 196i, Ser. No. 92,069 lillClaims. (Cl. 1791l3) This invention relates to an inertialess transducerand more particularly to a device which can convert electrical energyinto radiant energy and is an improvement upon the constructiondiscltosed and claimed in United States Patent No. 2,768,246, issued onOctober 23, 1956 to Siegflied Klein. The construction disclosed in saidpatent generally comprises a means for generating a gaseous dischargewithin a small cell exposed to atmosphere. This discharge is created andmaintained by high frequency electric currents which can be modulated bysuitable signal currents. The discharge emits a wide spectrum ofelectromagnetic radiation ranging from infra-red through visible lightto ultraviolet. This radiant energy, when generated within a cellforming part of a horn such as disclosed in the patent referred toabove, is emitted in the form of a iine pencil.

In addition to the emitted rays, it is believed that the temperature ofthe gas or air yat the discharge region is also varied in a rapid mannerby the modulations. Such temperature variations appear to be responsiblefor pressure variations in the gas. By providing sufficient couplingbetween the discharge region and the atmosphere, it is possible togenerate pressure waves in the atmosphere corresponding to themodulating waves. There does not appear to be any definite top or bottomlimits to the frequency range `of such pressure waves. In practice,waves below about 3,000 cycles per second require an undesirably longcoupling horn between the discharge region and atmosphere, so thatdevices of this type for converting electrical energy into sound wavesare most conveniently designed for operation at frequencies above 3,000or 3,500 cycles per second. It is understood, however, that such devicescan operate with lower frequencies insofar as sound is concerned, if thesize and expense of a coupling horn are disregarded. `It is, of course,understood that the cell containing the discharge region must be ofelectrically insulating material. The high temperatures existing at thedischarge region require that the envelope be of refractory material.For long life, quartz has been found to be best.

The manufacture of quartz parts, without subsequent i grindingoperations, lcan not be accomplished to close dimensional tolerancescomparable to metal working. In fact, it has been found that dimensionalvariations of the order of as little as .020 in a quartz cell result inlarge variations in the electrical and acoustic characteristics of atransducer. This has reacted upon the electrical accessories, as theoscillator for' example, and has required custom adjustments. The samehas been true of the acoustic portions, as the horn.

While the present invention in general relates to an improved transducerand 4the manufacture thereof in quantity, there are a number of facetsto the overall invention. First and foremost is a practical andeconomical method of manufacturing quartz cells to close tolerances.Second is the structure of a transducer which has desirable andpredetermined operating characteristics. Such characteristics includethe generation and maintenance of a stable gaseous discharge within thecell, these at generally predetermined potentials. Furthermore, thetransducer structure is quite efficient in that leakage of Vibratoryenergy is reduced to a minimum. Whether the transducer is used foracoustic purposes or as a generator of high frequency electro-magneticwaves (infra-red or light as two examples) the present invention makespossible economical production as well as reliable use of what may betermed van ionic inertialess transducer.

The more general as well as specific aspects of the present inventionwill be more readily appreciated and understood when presented inconnection with a description of the invention and reference to thedrawings.

FIGURE 1 is a perspective view of the new transducer.

FIGURE 2 is a section on line 2-2 of FIGURE l.

FIGURE 3 is a section detail on line 3 3 of FIG- URE 2.

FIGURE 4 is enlarged sectional detail of the inner electrode and itsrelation to the cell.

`FIGURE 5 is a view illustrating apparatus for drilling the quartz, thisfigure showing the bit for shaping the discharge chamber within thecell. f

FIGURE 6 is a view generally similar to FIGURE 5 but showing the bit andcell enlarged.

FIGURES 7 and 8 show the bits used in connection with other drillingoperations on a quartz cell blank.

The transducer unit proper consists of cell 10 of refractory insulatingmaterial, inner or center electrode 11 and outer electrode 12. Thetransducer unit has coupling member 14 of insulating material forcoupling the transducer to a horn, not shown. This horn, as pointed outin the Klein patent referred to, may taper to provide acoustic couplingto atmosphere or any shape may be used simply to provide a path toatmosphere of the radiant energy generated by the discharge. As theinvention is not concerned with the horn, no further description isnecessary.

As is described in the Klein patent, a radio-frequency oscillatorapplies potentials to the two electrodes and generates and maintains agaseous discharge within the cell. The RF. applied to the electrodes canbe modulated at lower frequencies and cause the arc intensity to vary atmodulating frequencies. The variation in intensity of the dischargeresults in the generation of waves in the gas, usually air, within thecell and such waves can be transmitted to atmosphere.

insofar as manufacture to close tolerances is concerned, the problem isfocused on cell 10i. This cell is made of quartz to a high purity.Bcause of the hardness of quartz and close tolerances of concavesurfaces, conventional grinding technique was too expensive for quantityproduction. The actual method of manufacture of the cell will bedescribed later.

Cell 10 has outer cylindrical surface 18, front (horn) end 1.9 and rearend 20. It has been found that at high audio frequencies (over 10,000cps.) and ultra audio frequencies, undesired leakage of vibratory energyat joints can easily occur. Accordingly, end faces 19 and 2@ must beaccurately iitted to the remaining parts of the unit. This is mosteasily accomplished in quantity production by having end faces 19 and 20flat -and perpendicuiar to the axis of cell i0. For transducers forhandling frequencies up to 20,000 c.p.s. or more, it is preferred tohave end face 19 :true to about 2. Such a tolerance will reduce leakageof vibratory energy to an inconsequential level. Outside surface I3 ofcell 10 should also be accurate, since it determines the ygeometry ofouter electrode 12.

Cell l0 has coaxial chambers v23 and 24 extending from end faces 19 and20 toward each other. Chambers 23 and 24 are joined together by passage25. Passage 25 is cylindrical and has circular ends 26 and 27. Thediameter of passage 25 is less than the transverse dimensions ofchambers 23 and 24 near the ends of the cell. Chamber 24 has acylindrical shape, `although this is not essential. Chamber `2li has`annular end wall 30 at end annales 27 of passage 25 :and hm cylindricalwall 31 extending to rear end face 2.0.

Chamber 23 conta-ins the ygaseous discharge and must therefore be madequite accurately. For use `as a trans- 23 has tapered portion 33extending from end 25 of passage 2S. f

The :taper is about 30 although this value is not critical. However itshould not be greater than 45 and no less than if desirable reproductionisto be provided. Portion 34 of chamber 23 extends from circular region35 to end face 19. Portion 34 of chamber 23 may also taper generallylinearly. This taper is smaller than for portion 233` and may be aboutTO3-20. The axial length of chamber portion 34 Will depend in somemeasure upon the ease with which a horn can Ihave its small endaccurately shaped. IIn practice, portion 34 may have an axial lengthequal to the maximum diameter of the cham- Y ber at end face 19.Discharge chamber portion 33 may have the end diameters in the ratio ofabout 2 to '1. Passage may have a length equal to or greater than itsdiameter. The dimensions or proportions of chamber 31 are not important.In general, the surfaces defining passage 25 and chamber 2?` should beaccurate to about .1002. The overall length of cell 1li and its outsidediameter are not important, `but what is important is the accuracy ofthese dimensions.

Referring now to inner electrode 11, this consists of head all'supported on neck 41 extending from shoulder 42 carried by a relativelymassive body portion. Except 'for head 4d, the remainder of electrode 11may be made of any metal or material which can conduct electricity.

Thus neck 41 or shoulder'42 or the body portion or all A of the Vthreemay be 'made of material like iron, copper or brass. electricalresistance .is unimportant since the amount of current carried isrelatively low. It is also possible to make neck 41 asia thermistor anddesign it so that the change of resistance, with respect to temperaturewill be sufficient to provide a current control action'. The toleranceson head 4@ and the massive body portion of the electrode 'will bedetermined generally by the cell tolerances.

Head 40, during a discharge, is maintained at a high temperature. Thematerial of head must be capable of Awithstanding a high temperature andfor transducer use 'should be .free of sputtering. Sputtering of :thehead metal results in generation of noise. In addition, the materialshould be easy to machine or shape. 'Ilhe material used for cigarettelighters in automobiles or as electrodes in auto engine spark plugs canbe use-d. Such metals as kanthal and itopheta A can be used. Thesemetals generally are alloys of iron and chromium and can Withstandtemperatures of labout lO'OO" C. in air. The remainder of the electrode'is conveniently of the same metal, although any metal may be used.

Head 49 has the shape of a truncated cone with sharp edges and `46 atthe front and rear of the head re- For most metals and'alloys, ythevariation of vtained in production to about .002.

, Y '4 Abody portion 51 smoothly merges into cylindrical terminalportion S4. Body portions 49 and 51 must be able to enter chamber 24 andthe electrode is preferably long enough to extendV beyond end face 2liof cell 1t);

ltwill be noted that in the assembled transducer circular edge 4d shouldbe disposed within passage 25 while edge 45 should be forwardly of end26of the passage. The clearance between yedgeV 46 and the wall of passage25 should be several thousandths of an inch. `Both edges 41S and 46 aresharp. The taper of head 40 can be about 3d, although this is notcritical. However, a tapered head is important. y

lt has been found that a discharge will start easily along kan edge ofthe head. lf a flat head with no taper is provided, then the dischargeis unstable and tends to wander along the surface of the head. The coneshaped head stabilizes the discharge and tendsk to keep it in oneposition. 'Ille sharp edges make it easier to initiate a discharge. Y

. The relative mass ofhead 40* and neck 41 will determine how quicklythe head will heat and temperature at which it will stabilize itself.The heat dissipation characteristics will depend upon the geometry ofthe electrode, availability of kcirculating air to the electrode andalso the amountof RF. energy fed into the system. It will be understoodthat inner electrode 11 is pressed firmly into position. It need not becemented.

Outer electrode V12-is of any metal, as spring brass, copper orstainless steel. Guter electrode 12 is in the shape of a split cylinderhaving slot all extending longitudinally thereof. It is Yimportant tohave the inside edges of electrode 12 free of burrs. This will permitelectrode 12 to lay snugly against outer surface 18 ofcell 10'. It isimportant to avoid air pockets between the cell and electrode, sincesuch pockets may have arcs'and result in noise as well as damage.Preferably outer electrode 12 is so disposed that its rear edge A62 willbe offset rearwardly of edge 46 of inner electrode 11 for maximumefficiency. The amount of offset is not critical, but should be mainlThe location of forward edge 63 is not critical and this can be flushwith end face 19 of cell 10.

The slit in the outer electrode permits of expansion of the metal duringoperation without cracking coupling insulator sleeve 14. Coupling sleeve`1.4 has rear face 66 provided with chamber 67 dimensioned toaccommodate outer electrode Y12. The outer electrode is preferablycemented into coupling sleeve 14. 'The edge of the material at chamber67 at face 66 is cut away for countersinking. Chamber 67 has bottom wall68 flat and this must be as accurate as front face 19 of cell 1G'. Anyradial Y path yalong face 19 will permit energy to escape.

spectively. The diameter of edge 46 is a bit less than Coupling sleeve14 has tapered axial passage 7d extendingfrom wall 68 to front face 71of the sleeve. Passage 70 at small end 73 registers with and is alinedwith chamber 23 of cell 1l). The front portion of sleeve 14 isshouldered at '75y for accommodating metal or plastic horn '76'. Sleeve14 may be of ceramic, glass, plastic, or any insulating material. MetalVsupport plate 77 is disposed around a portion of the horn for supportingthe entire transducer.

The accuracy of the electrodes, cell 1lil and sleeve 14 Y is directedtoward providing smooth, snug fits with minimum tendency of cooking ofany parts. By maintaining good alinement, uniform field distribution isobtained. In -the -assembly so far described, cell 10 and innerelectrode 11 are readily separated from each other and' from outerelectrode 12. It is therefore important to provide means for maintainingthe parts in alined relation during operation.

The transducer parts are maintained in operative posiv tion by thefollowing. Metal cap 80 iits over portion 54 of inner electrode 11. Cap80l has wire 81 attached thereto as one terminal. Wire 82 attached ktoelectrode 12 is the other terminal of the transducer. Cap 80 hasshoulder 84 providing reduced portion 85. Insulator bar 86 is aperturedto accommodate reduced cap portion 85 and is urged forwardly (toward thehorn end) by springs 38 and 89 having ends attached to the ends of bar86 and flanges 90 and 91 of metal plate 92 rigidly attached to plate 77.It is understood that plates 77 and 92 are tight enough on horn part 76to withstand the pull of the springs. If desired, a three point supportfor cap 80 may be provided instead of two points. Thus a three leggedspider with legs symmetrically disposed may be used with springs toprovide a balanced force on cap 80 axially of the cell. The arrangementshown is convenient and permits easy replacement of the cell or otherparts. Bar 86 can be pulled away from the cap and swung out of the way.

As has been previously indicated, the economical manufacture ofA quartzcells to close tolerances of the order of .00 for interior surfacespresented serious problems. For example, in a practical device, passage25 has a diameter of .060 with a tolerance of plus or minus .0012". Themaximum diameter of chamber 23 is .150 plus or minus the same tolerance.Making the quartz cell to close tolerance insofar as length and outsidediameter are concerned presented no particularly serious problems.However, manufacturing the quartz cell to the desired internaltolerances presented serious production problems. The only practicalmethod for drilling involved the use of ultrasonic equipment. As is wellknown, this equipment involves the phenomenon of magnetostriction. Thuscertain ferromagnetic materials such as certain nickel-iron alloys areparticularly for this purpose. When a rod of this material is subjectedto a magnetic field Whose intensity varies at a suitable frequency, suchas for example, 30,000 c.p.s., the length of the rod will vary by -asmall amount.

It is well known in ultra-sonic drilling that the drill bit must bemuchI softer than the work. Bits of soft metal such as soft steel oriron or brass are frequently used and it is customary to braze a bit tothe end of the magnetostrictive rod. The bit Working with a slurry offinely divided abrasive in water or oil is used to operate on the work.

In prior ultra-sonic drilling, it is customary to use the bit to operateupon a substantial number of pieces of material-constituting the work.When the Wear on the bit was sufficient, it was necessary to remove thebit and braze a new bit in position.

In -the application of ultra-sonic drilling and grinding to quartz forthe manufacture of cells to desired tolerances, it was found that thisprocedure of using the same bit for a substantial number of quartzpieces of work was not dependable. It was dicult to manufacture cells tothe required tolerances and the drilling costs including time were veryhigh."

Replacing brazed bits at frequent intervals to improve tolerances of thefinished product resulted in extensive time for brazing new bits intoposition. Trying to save brazing time results in excessive drilling timewith poor control yover the quality of the finished work.

In accordance with the present invention, both problems weresimultaneously solved by making an expendable bit which could be quicklyand easily replaced. It was found that if a certain operationalprocedure with regard to drilling the cells was adopted that theproblems of quality control of the work as well as quick replacement ofthe bit were solved. This was accomplished generally by designing thebit as a screw machine product which could be automatically manufacturedin large quantities and having a screw coupling as the attaching meansfor the bit to the magnetostrictive rod.

Screw couplings for bits in ultra-sonic dril-ling have not previouslybeen considered practical. This is because the combination oftemperature changes and vibration tend to loosen the bit and thus reducethe efficiency of grinding to the vanishing point. In accordance withthe present invention, however, theprevious Vdisadvantage regardingfrequent bit replacement is utilized to render the use of a screwcoupling for the bit practical. This however, was only possible byutilizing a novel drilling technique. This techniques consists inutilizing a new but expendable bit purely to finish a previously roughedcell to final dimensions. The roughing for the discharge chamber of thequartz blank may consist in drilling to within about .004 inch of thedesired dimensions. Thus a brand new bit is only used to cut out aboutthis amount of quartz. Thereafter, the partly used bit Wil-l be appliedto rough out a different quartz blank, after which the bit can bediscarded.

It is clear, therefore, that a bit designed for screw machinemanufacture and susceptible to being quickly screwed on or off greatlyreduces the drilling time and the time for changing bits, as Well asproviding a close control over tolerances in the finished product. It isunderstood that this technique has these advantages only because of theextreme hardness of quartz.

The various steps in the procedure of manufacturing a cell areillustrated in FIGURES 5 to 8 inclusive, of the drawings. It isunderstood that the quartz cell blank consists of a cylindrical member,the ouside of which has been ground to size, both with regard todiameter and length. For convenience, FIGURES 5 and 6 show the cellhaving the discharge region ground out. Thus, magnetostrictive rod isdisposed within winding 96. The winding is connected to a current sourceof ultra-sonic frequencies, these ranging anywhere from about 20,000cps. to as much as 100,000 c.p.s. The actual frequency used isdetermined by such factors as the size of the work and the character ofthe grinding operation.

Rod 95 has tapering portion 98 terminating at face 99. End 99 of the rodis provided with a threaded recess l0() axially of the rod. Disposed inrecess 100 is a drill bit of the shape desired. In FIGURES 5 and 6, theactive portion of the drill bit is shaped as illustrated, Drill bit 101has a threaded bolt portion which fits into threaded recess 100. Thedrill bit also has flange portion 02 which rests against flat face 99and body portion 103. The active portions of the drill bit will dependupon the nature of the operation. A slurry of finely divided abrasive inwater or oil as previously specified can be directed on the work bymeans of hose 105 and nozzle 106.

Thus referring to FIGURES 7 and 8, two drill bits are shown forrespectively drilling an axial passage through a quartz cylinder blankand then drilling or grinding chamber 31 in the blank. The initial axialpassage illustrated in FIGURE 7 Will ultimately form passage 25 in thefinished cell and will therefore be dimensioned accordingly. During thegrinding or drilling, it is important that the work be rotated slowlyaround the drill axis. This will prevent unevenness in the finishedwork. The rotation of the work or oscillation back and forth may beaccomplished manually by turning the chuck 108 into which the work ismounted by the ring handle or by turning the entire magnetostrictiverod.

When chamber 23 of the cell is to be drilled and ground, a bit which hasbeen previously used for finishing is used for roughing out purposes.After the chamber is roughed out to within about .002" to about .004,then a brand new bit is substituted. This brand new bit is then used forfinishing chamber 23 to size and this bit is now used for roughing outchamber 23 in a succeeding quartz blank.

Insofar as passage 25 or chamber 31 are concerned, a bit may be used onone or two blanks depending upon the amount of wear. It appears thatthese two steps, grinding passage 25 and chamber 31, do not appear to beas demanding as operating on the cell for producing chamber 23. Thus,with either passage 25 or chamber 311, there is no necessity for alwaysusing a new bit for a finishing operation. This is particularly true ofchamber 31 whose tolerances may be as much as .004. However,

tionship along the cell axis.l

the depth of chamber 3-1 is important and must be accurately controlled.This is principally due to the desired relationship'betweentheover-lapping edges of the outer and inner electrodes as previously setforth. Y l lt is possible to have the threaded bolt portion at the endof'the magnetostrictive rod and have a threaded recess in the bit.

j What is claimed is: f Y

1. A transducer comprising a cell of refractory electrically insulatingmaterial, said cell having a bore extending along the length thereofwith the. ends of the bore enlarged .to `form front and rear chambers,an inner electrode disposed within the rear chamber and having an activeelectrode portion projecting through the bore' and into thel frontchamber, an outer electrode disposed around the cell at the frontportion of the cell, said outer electrode enclosing'the portion of theVcell defining the frontjcharnber, said outer electrode being in the formof a split metal sleeve and an insulating member disposed around saidouter electrode, said cell, outer electrode and insulating member beingsnug, said outer electrode having room for expansion and means formaintaining said cell and electrodes in predetermined relation.

"bore and Van enlarged head portion extendingl from the front portion ofthe bore toward the second chamber, said head portion having the shapeof a truncated cone with the free endof said head constituting the:small end, the base of the cone extending laterally beyond the neck ofthe electrode and lying within the bore, an :outer electrode in the formof a metal member disposed around the cell, a second Vmember ofelectrically insulating lnaterial disposed around the frontrportion ofthe outer electrode and Vhaving a chamber therethrough communicatingwith the cell chamber.

7. The construction according to claim 6 wherein said outer electrode isin the'forrn of a metallic sleeve having 2. The transducer accordingV toclaim l wherein said Y means for maintaining said electrodes inpredetermined relation include means for impressing a spring bias onsaid inner electrode to urgesaid inner electrode forwardly and maintainthe transducer intact.

3. The construction according tc claim 2 wherein said means for creatingsaid spring bias includes an insulating member pressing against the rearendof said inner electrode and springs engaging said insulating memberto urge the same forwardly of the transducer.

4. A transducer comprising a cell of refractoryv elec- I tricallyinsulating material, said cell having a generally cylindrical borepassingthrough the length thereofy withk enlarged chambers at the frontvand rear portions of said cell, an inner electrode having a bodyportionvdisposed in said rear chamber and having an active electrodeportion extending forwardly through the bore and into said frontchamber, said active electrode portion including an electrode' headhaving the shape of a truncated cone with the head partly in the boreand partly'in the front cham-VV ber, the forward end of the head havinga` smaller `diam,- eter than the rear endof the head, an :outerelectrode disposed around the front portion of the cell, said outerelectrode having the general shape of a sleeve with the rear end of theelectrode overlapping the active head portion of the` inner electroderand the outer electrode extending forwardly around the front portion ofthe cell in which the frontchamber lies.

5. rThe construction according to claim 4 wherein said inner `electrodehas a shoulder engaging the cell material at the forward' endj of theonechamber to define Vthe position of said electrode andV whereinmeans'are provided for maintaining said electrodes Vcell in alignedvrelaa slot longitudinally to permit expansion thereof within the secondinsulating member.

8. The construction according to claim 6 wherein means are provided forspring pressing said inner electrode for# wardly of the transducer andaxiallyof the cell.

9. The construction according to claim 6 wherein said cell is of quartzand has the forward end thereof disposed against a portion of the secondinsulating member, the meeting surfaces thereof being accurately groundto minimize the escape of vibratory energy which may be generated by thetransducer in the other chamber and wherein saidY second lchamber has aconical portion with the cone angle being between about 20 and about 45for desirable'reproduction of audio frequencies'. f

10. A transducer comprising a quartz-cell having af bore terminating inchambers at the two ends of said cell,

'an inner electrode having a bodypportion within one -1,000 C withoutsputtering and an outer electrode consisting' of a metal member disposedaround the cell.

lil. The transducer according to claim l() wherein saidl innerelectrode' is an alloy containing chromium.

References Cited in thefile of this patent UNITED STATES PATENTS LevySept. 9,

10. A TRANSDUCER COMPRISING A QUARTZ CELL HAVING A BORE TERMINATING INCHAMBERS AT THE TWO ENDS OF SAID CELL, AN INNER ELECTRODE HAVING A BODYPORTION WITHIN ONE CHAMBER AND A PORTION IN SAID BORE AND TERMINATING INAN ACTIVE HEAD PORTION EXTENDING INTO SAID OTHER CHAMBER, SAID HEADPORTION HAVING THE GENERAL SHAPE OF A TRUNCATED CONE AND CONSISTING OF AMETALLIC MATERIAL WHICH CAN WITHSTAND TEMPERATURES IN AIR OF THE ORDEROF ABOUT 1,000*C. WITHOUT SPUTTERING AND AN OUTER ELECTRODE CONSISTINGOF A METAL MEMBER DISPOSED AROUND THE CELL.